Within the machining job space of a machine tool, as the position of a machining point is changed such that the load-carrying position of members of the machine tool and the magnitude of load (including force and moment) are changed, static stiffness of the machine tool is changed. Static stiffness changes at different machining positions may be described using stiffness distribution. The magnitude and distribution of the static stiffness directly affect the machining precision and the vibration characteristic of the machine tool.
The machined surface of a work piece is formed through a relative movement between a cutter and the work piece. The forming principle of the machined surface is divided into a trajectory method, a shaping method, a tangency method and a generation method. Depending on the different forming principles of the machined surface, the machine tool has a different movement function. For example, in terms of the gear grinding machine that grinds gears, the forming principle of the machined surface for the NC gear grinding machine with shaped grinding wheel employs shaping method, and thus the shape of the grinding wheel is the same as that of the tooth space of the gear; while the forming principle of the machined surface for the NC gear grinding machine with worm grinding wheel employs generation method, and thus the shape of the grinding wheel is a shape of the worm. Depending on the different types of the NC machine tool, the property of the load carried between the cutter and the work piece at the machining point, change rule of the loads at different machining positions and proportions among the loads in all directions are different, and thus simulating loading apparatuses used in various types of the NC machine tool and corresponding detection methods thereof are different.
Unlike the forming principles of the machined surface employing the trajectory method and the tangency method of a general NC turning machine and a machining center, as well as other machine tools that machine gear employing the generation method, the forming principle of the machined surface for the NC gear grinding machine with shaped grinding wheel employs the shaping method, and thus the simulating loading apparatus and corresponding detection method thereof are different from conventional apparatuses and methods.
Static stiffness test of the machine tool employs simulated load instead of cutting load. Taking NC gear grinding machine with shaped grinding wheel as an example, during machining, as position of the machining point moving in the Z, X, and C axes is changed, positions of components in the Z, X, and C axes are changed, such that both the static stiffness at one side of the spindle and the static stiffness at one side of the work bench will be varied along with change of the position of the machining point of the work piece. However, detection apparatuses and methods for static stiffness existing at home and abroad can only detect the static stiffness at one determined position, but can not detect static stiffness distribution.